net: ipv6: mld: implement RFC3810 MLDv2 mode only

RFC3810, 10. Security Considerations says under subsection 10.1.
Query Message:

  A forged Version 1 Query message will put MLDv2 listeners on that
  link in MLDv1 Host Compatibility Mode. This scenario can be avoided
  by providing MLDv2 hosts with a configuration option to ignore
  Version 1 messages completely.

Hence, implement a MLDv2-only mode that will ignore MLDv1 traffic:

  echo 2 > /proc/sys/net/ipv6/conf/ethX/force_mld_version  or
  echo 2 > /proc/sys/net/ipv6/conf/all/force_mld_version

Note that <all> device has a higher precedence as it was previously
also the case in the macro MLD_V1_SEEN() that would "short-circuit"
if condition on <all> case.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 005b22f..c916568 100644 (file)
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1112,11 +1112,34 @@ static bool mld_marksources(struct ifmcaddr6 *pmc, int nsrcs,
        return true;
 }
 
+static int mld_force_mld_version(const struct inet6_dev *idev)
+{
+       /* Normally, both are 0 here. If enforcement to a particular is
+        * being used, individual device enforcement will have a lower
+        * precedence over 'all' device (.../conf/all/force_mld_version).
+        */
+
+       if (dev_net(idev->dev)->ipv6.devconf_all->force_mld_version != 0)
+               return dev_net(idev->dev)->ipv6.devconf_all->force_mld_version;
+       else
+               return idev->cnf.force_mld_version;
+}
+
+static bool mld_in_v2_mode_only(const struct inet6_dev *idev)
+{
+       return mld_force_mld_version(idev) == 2;
+}
+
+static bool mld_in_v1_mode_only(const struct inet6_dev *idev)
+{
+       return mld_force_mld_version(idev) == 1;
+}
+
 static bool mld_in_v1_mode(const struct inet6_dev *idev)
 {
-       if (dev_net(idev->dev)->ipv6.devconf_all->force_mld_version == 1)
-               return true;
-       if (idev->cnf.force_mld_version == 1)
+       if (mld_in_v2_mode_only(idev))
+               return false;
+       if (mld_in_v1_mode_only(idev))
                return true;
        if (idev->mc_v1_seen && time_before(jiffies, idev->mc_v1_seen))
                return true;
@@ -1223,7 +1246,6 @@ int igmp6_event_query(struct sk_buff *skb)
                return -EINVAL;
 
        idev = __in6_dev_get(skb->dev);
-
        if (idev == NULL)
                return 0;
 
@@ -1236,6 +1258,10 @@ int igmp6_event_query(struct sk_buff *skb)
                return -EINVAL;
 
        if (len == MLD_V1_QUERY_LEN) {
+               /* Ignore v1 queries */
+               if (mld_in_v2_mode_only(idev))
+                       return 0;
+
                /* MLDv1 router present */
                max_delay = msecs_to_jiffies(ntohs(mld->mld_maxdelay));